The present invention relates to microelectronic transmitters, particularly to their structure and operation.
High-speed microelectronic serial data transmitters can transmit at rates of multiple gigabits per second (Gbs) and even tens of Gbs. Such high-speed serial transmitters typically are implemented on microelectronic elements, e.g., semiconductor chips, with several transmitters implemented on each microelectronic element.
The bandwidth of a transmitter refers to a range of frequencies for which the output of the transmitter has about the same amplitude. Ideally, the bandwidth of a serial data transmitter should stay constant throughout the range of operating conditions that the transmitter encounters. Maintaining bandwidth helps to reduce energy consumption and can reduce cross-talk noise between adjacent transmitters on the same microelectronic element.
Sometimes, a transmitter design is required to accommodate different customer specifications with a wide range of data rates. A one-design-fits-all practice has become a norm for the semiconductor industry to save design cost. However, transmitters designed this way can sometimes have difficulty meeting the bandwidth requirements for transmission at the highest data transmission rates.
FIG. 1 contains Bode plots (curves) illustrating an amplitude versus frequency response of a prior art serial transmitter under different operating conditions. Curve 10 is a graph illustrating nearly ideal amplitude versus frequency response for the transmitter. In this case, the amplitude is fairly constant at amplitude a0 in the frequency range f0 to fmax. The frequency response exhibited by curve 10 will result under a fairly narrow range of operating conditions, such as when the temperature of the microelectronic element and the voltage level of the power supply voltage supplied to the transmitter are close to ideal. Unfortunately, operating conditions, including temperature and power supply voltage level are frequently at levels which are not close to ideal. The temperature may vary between subzero temperatures upon powering up the transmitter in cold locations to over 100 degrees C. in some densely packed environments. The power supply voltage level may also vary, for example, between 1.0 V and 2.5 V (by as much as 150%). Curve 12 illustrates a frequency response of the transmitter under different, non-ideal operating conditions, for example, when temperature is elevated and the power supply voltage level is decreased. As illustrated by curve 12, the frequency response under the non-ideal operating conditions worsens. The amplitude rolls off (decreases) at a lower frequency (fR) than fmax, such that bandwidth under the non-ideal operating conditions is impacted. At frequency fmax of the curve 12, the amplitude has already fallen from the initial amplitude a1 to a decreased amplitude a2, for a total decrease in amplitude of Δa. It is difficult, if not impossible, to design a serial data transmitter which has satisfactory frequency response under the different extremes of operating conditions.